Ultraviolet lamp systems are commonly used for heating and curing materials including adhesives, sealants, inks, and coatings, as well as optical cables and tubing. Certain ultraviolet lamp systems have electrodeless light sources and operate by exciting an electrodeless plasma lamp in a processing chamber with radiofrequency energy, such as microwave energy. In an electrodeless ultraviolet lamp system that relies upon excitation with radiofrequency energy, the plasma lamp emits a characteristic spectrum isotropically outward along its cylindrical length. Part of the emitted radiation moves directly from the plasma lamp toward a substrate located in the processing chamber. A substantial portion of the emitted radiation must be reflected before reaching the substrate. To efficiently use the ultraviolet radiation emitted by the plasma lamp, various designs of reflectors have been mounted in processing chambers to surround the plasma lamp and the substrate.
While conventional reflectors include rectangular box-shaped reflectors and parabolic reflectors, the most efficient reflector system is an elliptical reflector. By placing the plasma lamp along one focus of the elliptical reflector and the substrate at the other focus of the elliptical reflector, all radiation emitted by the plasma lamp reaches the substrate after no more than one reflection. Examples of these conventional systems with elliptical reflectors include U.S. Pat. No. 4,710,638 issued to Wood and U.S. Pat. No. 6,626,561 issued to Carter, et al. One challenge of conventional systems is that the efficiency of irradiation decreases as the diameter of the substrate increases because the substrate moves away from the focal axis. Therefore, the use of a completely elliptical reflector limits the diameter of the substrate being treated. Another shortcoming of conventional systems is that the substrate is often enclosed within a quartz or other ultraviolet-transmissive conduit to protect the substrate or a coating applied to the substrate from contamination. The substrate should not contact this ultraviolet-transmissive conduit, making threading the substrate through the processing chamber difficult.
It would be desirable to provide an efficient curing system with reflectors that allow for generally efficient irradiation of elongate, continuous substrates having a wide range of diameters. It would also be desirable to provide a curing system that eases the process of loading such substrates into the processing chamber.